I have a motto myself, "If it ain't free, I probably don't want it... If it IS, get outta my way, 'cause it really hurts getting trampled by 260lbs."
hehehe...
Also look for overturned trees, or loose stumps. Root wood is more water resistant and looks sooooo cool.
If you have an eye for mopani wood like I do, you can find GREAT deals on large pieces at Petco. The medium sized pieces list for 9.99, and MOST of the large pieces are mismarked as medium. Plus, it goes on sale almost constantly. I've gotten three pieces now for 5 bucks or less apiece.
Keep an eye on craiglist (is there an equivalent in Canada? I forgot you weren't in the US when I wrote this... The seahawks thing is throwing me off and making me think you're here around Seattle, lol) for people getting rid of driftwood too. Sometimes it's free, sometimes it's really cheap. I got two huge pieces for 10 bucks.
Go hiking, you can find great pieces in the woods. It doesn't just have to be driftwood. I usually take something to use as a saw or whatever in case I find a branch ON a tree that I just have to have. I know, people say not to take live branches, but I do, and I still will, even when they say I shouldn't, lol... If I can find dead stuff I like better, that's great, but sometimes the live stuff is just what I want (and easier to bend if necessary).
Also, if you spot someone doing landscaping, stop and ask them if you can go through the pile of branches before they chip them. Sometimes you can find great pieces that would otherwise be turned into mulch. Bigger branches can always be cut down (which they may do for you if they aren't terribly busy).